Propose an open ended study in adult subjects on chronic TPN. This study will involve 24 hour parathormone profile on and off calcium supplementation in the TPN, 2 hour parathyroid challenge test, measurement of bone dynamics by Positron Emission Tomography (PET) scan with 18F Fluoride ion, Bone density by Dual Energy X-ray Absorptiometry (DEXA) scan and bone histopathology.